Continuous data protection enables a user to be able to access or restore a previous state with finer time granularity than previously offered by some traditional backup solutions. For example, some traditional backup solutions perform backups at discrete points in time that are separated by hours or even days. The only previous states that a user is able to restore are the states corresponding to those points in time. With continuous data protection, data (e.g., a file or other data associated with a continuously protected device) is continuously protected over a window of time and a user is able to access almost any prior state within that window. For example, using some continuous data protection systems a user can access or restore saved states that are seconds or fraction of seconds apart.
To continuously protect data, previous version data is obtained and stored. Typically, storage used to store previous version data is reclaimed as the data stored in particular locations is no longer required to be retained, e.g., because it relates to states that fall outside (i.e., prior to the earliest/beginning edge of) the rolling window described above. However, in some cases previous version data that falls outside the continuous data protection window may need to be retained, e.g., because a user has indicated the data is desired to be available to be used to restore a data set or one or more data objects comprising the set. In some cases, storage locations that would otherwise be eligible for reclamation and reuse contain previous version data still required by two or more independent owners, e.g., previous version data associated with data blocks that were not changed between a time t1 associated with a first mounted restore point and a later time t2 associated with a second mounted restore point. Therefore, there is a need for a way to prevent efficiently reclamation and reuse of storage locations in which previous version data that has fallen outside the continuous data protection window but which still is required by two or more independent owners is stored.